In the event of a fault in or during maintenance of a photovoltaic system, it is not possible to interrupt a photovoltaic system which is exposed to light in such a way that the individual strings of photovoltaic modules now only produce a voltage below the so-called protection voltage. Disconnection of the feed from the grid results in the photovoltaic module strings transferring to no-load operation and thus a system voltage of up to 1000 Vdc may be established.
In order to counteract this situation, various proposals have been developed:
DE 10 2005 018 173 B4 discloses limiting the energy output of a complete generator field at the entry point into the building. This means that hazardous voltages outside the building cannot be avoided.
Furthermore, DE 20 2006 007 613 U1 describes incorporating thermal fuses into the connecting lines between the photovoltaic modules. However, this does not have any effect which is necessarily and simultaneously for the entire generator field.
In addition, DE 10 2006 060 815 A1 describes integration of switching elements in the so-called junction boxes of photovoltaic modules which, in the event of a fire, limit an energy output of all of the photovoltaic modules at the same time and thus avoid a hazardous voltage.
In addition, according to DE 10 2008 003 272 A1, signal transmission may take place with modulation over the DC connecting lines or over a separate signal line or by radio transmission.
Furthermore, it is known from WO 2004/107543 A2 to disconnect photovoltaic modules manually for installation and maintenance purposes with a control signal.
Finally, DE 10 2010 017 746 A1 describes dividing the series circuit in order to get down below a protection voltage of 60 V. This results in a combination of a series circuit and a parallel circuit for transporting the signal even in the case of isolated photovoltaic module strings. However, one problem here consists in the use of the proposed technology with different impedances of the connected system. Furthermore, the operating costs for the monitoring unit decrease the yield of such a system.